Method for optical data storage and optical data storage media

ABSTRACT

In a method for optical data storage with high density, there are employed as the data carrying medium a number of flat, thin memory components in the form of cards or discs. Two or more of the memory components are arranged in a stack, thus enabling each individual memory component to be manoeuvred in relation to the other memory components by means of a manoeuvring device, and a given memory component is moved in relation to the other memory components in the stack in order to write or read data in a data carrying area on the memory component, which can be addressed optically during the write or read operation without interference from the other memory components. A data carrying medium for use with the method for optical data storage with high density comprises a number of flat, thin memory components in the form of cards or disks. A memory component comprises one or more data carrying areas, each data carrying area being capable of including one or more information carrying layers and arranged for optical storage of data. Furthermore, outside the data carrying area(s) the memory component comprises one or more optically transparent areas or windows.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method for optical data storage with highdensity, wherein there are employed as a data carrying medium a numberof flat thin memory components in the form of cards or disks, whereineach component comprises one or more information carrying layers,wherein each memory component has one or more data carrying areas whichare including one or more of the information carrying layers and adaptedfor optical data storage, and wherein the method comprises arranging twoor more of the memory components in a stack, thus enabling eachindividual memory component to be maneuvered in relation to the othermemory components by means of a maneuvering device. The invention alsoconcerns a data carrying medium for use with the method for optical datastorage with high density, wherein the data carrying medium comprises anumber of flat, thin memory components in the form of cards or disks,wherein each memory component comprises one or more information carryinglayers, and wherein each memory component comprises one or more datacarrying areas which are including one or more of the informationcarrying layers and being adapted for optical storage of data.

2. Description of the Prior Art

In to-day's digital, optical data storage media information is stored ina flat layer on a disk, a card or tape. Circular disks or a rectangularcard format are normally used. Even though the data density per areaunit in the storage layer is very high, the effective volumetric storagedensity is not correspondingly high. Each disk or each card has only oneor two data storage layers at the most and is typically 0.7-2 mm thickin order to provide the necessary rigidity and flatness for write/readoperations. Moreover, when such media are placed in a protectivecassette, there is a further increase in the volume. Even in the case ofso-called "floppy" optical Bernoulli disks which have recently beenproposed, the volumetric density is limited by the still substantialvolume of the actual floppy disk's substrate, as well as the requirementfor a protective housing or sleeve to cover the disk. The limitingeffect of the packing on the volumetric density in connection withfiling is particularly obvious in libraries which store CD cassettes.

The information carrying layer on present optical data storage media isthin, typically much less than 1 μm. Thus only a small fraction of thevolume of the disk or card is used directly for the data storageprocess. This is also the case even if the protective housing or sleeveis disregarded.

If it were possible to use the entire volume in a typical disk or a cardfor optical data storage, with a density which corresponded to thatwhich at present can be achieved per area unit, this would be ofsubstantial importance. By extrapolating from an area density which forexample corresponds to a bit spacing of 1 μm, the volumetric densitycould be 10⁹ bit/mm³. In a number of countries considerable efforts havebeen made to achieve digital, optical data storage within the volume ofa data medium. A number of different methods have been proposed for thispurpose:

(a) Holographic methods, in which refraction index changes are coded andread in the bulk material;

(b) three-dimensional positioning of bit points in a volume-fillingpattern within a bulk material, selective positioning being, achieved bymeans of sharp focusing of a laser beam, a non-linear response in themedium or an excitation on several wavelengths,

(c) stacking of a number of flat information carrying layers close toone another in a uniform structure which may be a simple bulk materialor a number of thin substrates which are attached to one another inorder to form a sandwich structure.

Of these above-mentioned methods, (a) and (b) appear to have thepotential for the highest volumetric data density, but at the presenttime they are far from being capable of practical implementation, notleast in equipment which should not be too expensive. In connection withthe method described under (c), several different techniques are thesubject of research and development, cf. the examples mentioned in thefollowing. Even though these techniques appear to have the potential toincrease data capacity on each disk or card up to tenfold, they allsuffer from the drawback that the carrying substrate has to bemanufactured within very strict optical and mechanical tolerances. Inaddition to the fact that this males for increased costs, there willalso be a good chance that the individual component will be of asubstantial thickness. The following examples of the state of the artand development trends will now be briefly discussed.

(1) A sharply focused laser beam with small depth of field can address anumber of information carrying layers at different depths under thesurface of a disk or a card by moving the focal point along the laserbeam's axis, by analogy with confocal microscopy. At each depth level athin optical storage layer must be provided in the disk's bulk material,e.g. by forming a dedicated plane structure. The absorbing, reflectingand transmitting properties for each layer must be carefully adapted andcontrolled in order to avoid crosstalk and covering up the deeper-lyinglayers. At present it is not clear to what extent these requirementslimit the number of layers which can be used in practice. It appears tobe obvious that the very stringent requirements regarding the flatnessand optical quality of the disk or card cancel out some of the benefitswhich are obtained with a monolithic structure.

(2) IBM recently presented a solution which resembles that which isdescribed in the above example, but with a composite disk consisting ofa number of thin disks which are joined together to form a sandwichstructure, and each of which is equipped with an information carryinglayer. Once again the optical properties of each layer must be carefullymatched in order to avoid crosstalk and covering up. According to IBM itshould be possible to stack up to ten layers in this manner. However,the composite disk is relatively thick and does not appear to be welladapted to the market requirements for inexpensive data carriers in acompact and practical format.

Finally it may as further examples of prior art be referred to that fromGB patent No. 1 184 657 there is known a data storage medium with anumber of photographic data storage elements in form of planarphotographic transparencies which are displaced to selected positionsfor addressing and from EP-A1-0 293 495 an optical memory device withoptical data carriers, for instance in form of cylinders which areguided in a container with an optical transparent window and therein canbe displaced in translation and rotation for addressing from an opticalwrite/read device.

Further there is from U.S. Pat. No. 3,800,942 known an informationretrieval device comprising a multiplicity of jackets each forcontaining an information card carrying picture information, a pluralityof magazines each for containing a plurality of such jackets, a drum forsupporting a plurality of such magazines in juxtaposition and a meansfor transporting the magazines on the drum at random to a selector meansfor thereby to retrieve a desired information card from a desiredmagazine transported to the selector means. The device is mechanicallycomplicated, as each magazine must be transported to the selector meansbefore the information card can be retrieved.

As further examples of prior art there may be referred to that from GBpatent No. 1,184,657 there is known a data storage medium with a numberof photographic data storage elements in form of planar photographictransparencies which are displaced to selected positions for addressingand from EP-A1-0 293 495 an optical memory device with optical datacarriers, for instance in form of cylinders which are guided in acontainer with an optical transparent window and therein can bedisplaced in translation and rotation for addressing from an opticalwrite/read device.

Finally, it should also be mentioned that players for playback of agramophone records and CD records may be equipped with facilities forautomatic record changing. This is usually done by arranging the recordsin a stack-like configuration and extracting a record from thestack-like configuration for playback. The stack-like configuration maybe contained in a magazine, as in the case in juke boxes and some CDplayers. However, in order to be manoeuvred and transported to theplayback device, the records in the stack are physically separated andmagazines for playback devices of this kind tend to be quite voluminous.However, International Published Patent application WO88/03694 disclosesa record player for CD records stacked in a magazine and wherein arecord is only partially extracted from the magazine in order to engagewith drive mechanism for playback. The same principle could easily wellbe applicable in a CD ROM player with a magazine for CD ROMs. The driveand read means will in any case be located outside the magazine as therecord must be freely rotated in the reading operation.

Further it should also be mentioned that players for playback of agramophone records and CD records may be equipped with facilities forautomatic record changing. This is usually done by arranging the recordsin a stack-like configuration and extracting a record from thestack-like configuration for playback. The stack-like configuration maybe contained in a magazine, as is the case in juke boxes and some CDplayers. However, in order to be maneuvered and transported to theplayback device, the records in the stack are physically separated andmagazines for playback devices of this kind tend to be quite voluminous.However, International Published Patent application WO88/03694 disclosesa record player for CD records stacked in a magazine and wherein arecord is only partially extracted from the magazine in order to engagewith drive mechanism for playback. The same principle could easily wellbe applicable in a CD ROM player with a magazine for CD ROMs. The driveand read means will in any case be located outside the magazine as therecord must be freely rotated in the reading operation.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide a methodwhich can be used in optical data storage with high density and use andespecially in a form of volumetric storage. Another object of theinvention is to provide a data carrying medium which can be used withthe method in order to permit a satisfactorily high, volumetric storagedensity.

A further object of the invention is that a method and data carryingmedium of this kind should meet a requirement for cost-effective datastorage systems implemented in a compact and user-friendly format.

The above-mentioned and other objects are achieved with a methodaccording to the invention which is characterized by providing one ormore optically transparent areas or windows on each memory component,thus forming a window area in the stack, each window being arranged anddesigned in such a manner that the windows are aligned with one anotherwhen the memory component is arranged in the stack, displacing a givenmemory component in relation to the other memory components in the stackin translation or rotation, such that a data carrying area on the givenmemory component is aligned with the window area in the stack andwithout the displacement causing the memory component to be separatedfrom the stack, whereby one or more of the data carrying areas on thedisplaced memory component wholly or partly can be exposed for readingor writing by means of the maneuvering device in order to write or readdata in the data carrying area or areas, the memory component in thewrite or read operation being addressed optically without interferencefrom the other memory components in the stack.

A data carrying medium according to the invention is characterized inthat the memory component outside the data carrying area or areascomprises one or more optically transparent areas or windows, the windowhaving a geometric shape corresponding to the shape of data carryingarea.

In a preferred embodiment of the data carrying medium two or more memorycomponents are arranged in a stack and each memory component is adaptedto be maneuvered in relation to the other memory components by amanoeuvring device.

Further advantageous embodiments of the invention are disclosed in thedependent claims. The invention will now be explained in more detail inconnection with exemplary embodiments and the attached drawing.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1a, b illustrates a first embodiment of the method and the datacarrying medium according to the invention.

FIGS. 2a, b illustrates a second embodiment of the method and the datacarrying medium according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIGS. 1a, b a first embodiment of the invention is illustrated inwhich the stack of card-shaped memory components or cards is seen incross section in FIG. 1a and from above in FIG. 1b.

Further FIGS. 1a, b show how a memory component for a write/readoperation is extracted only partially from the stack, thus exposing atleast a data carrying area on the card for writing/reading and withoutseparating the card physically from the stack. The card-shaped memorycomponent, referred to only as the card in the following, whichcomprises one or more not shown data carrying areas, can now, forexample, be identified by means of one or more optically readableidentification marks provided on the card, whereupon a not shownwrite/read device is employed to write or read data in the data carryingarea(s) on the card. Subsequently, as shown in FIG. 1b, the card isreturned to its original position in the stack.

It should be understood that each card or each memory component in thestack contains at the most one or only a few information carryinglayers, but as opposed to the above-mentioned prior art, the cards inthe stack according, to the method in the invention are naturally notimmovable in relation to one another. It will be seen that during thewrite/read operation a given card can be addressed optically without anyinterference whatever from the other cards in the stack.

As shown in FIGS. 1a and 1b there are in each card provided one or moreoptically transparent areas or windows which substantially correspond inshape and extent to a data carrying area on the card. When the cards arearranged in a stack, these windows in each card are aligned with oneanother, thus forming a window area in the stack. By now moving a givencard in the stack, a data area on this card can be placed in the windowarea in the stack and optically read without interference from the othercards in the stack, through the window area in the stack by means of awrite/read device located outside the stack. Thus the card does not needto be extracted from the stack, but is after a write/read cycle pushedinto the stack, whereupon the write/read operation with extraction of asecond card can be repeated. The windows in each individual card can bemade of an optically transparent material, but they can also simply be athrough in the going opening card. Several such windows can naturally beprovided in each card, e.g. alternating with data carrying areas and insuch a manner that several data carrying areas can be written or readsimultaneously through respective corresponding window areas, a numberof write/read devices being, employed which thus corresponds to thenumber of window areas in the stack.

The use of a data carrying medium with memory components with opticallytransparent areas or windows can easily be adapted to a method where themovement of the memory component in relation to the other memorycomponents in the stack is not performed by translation, but rather byrotation. In this case the memory component may preferably be designedas an optical disk and the appearance of the stack is as illustratedfrom the side in FIG. 2a and in a plan view in FIG. 2b. The memorycomponents in a circular, disk-shaped stack are again arranged in such amanner that the windows in the individual disks are in alignment withone another and form a window area in the stack. By rotating a disk inthe stack independently of the other disks, a data carrying area on theformer can be placed in the stack's window area and written or readtherethrough by an optical write/read device and without interferencefrom the other disks in the stack. Here too several windows can beprovided in each disk, thus enabling the write/read operation to beundertaken by performing a sector movement of the disk, e.g. over 90' inthe case of four windows in the disk. Alternatively a number of windowscan also here be used in each disk, providing alternating windows anddata carrying areas and allowing reading to be carried out when the diskhas performed an angular movement which locates the respective data areain alignment with corresponding window areas in the stack. Simultaneouswriting/reading can thus be undertaken since separate write/read devicesare provided in a number which corresponds to the number of window areasin the stack.

For the sake of simplicity the stacks are illustrated in all the figureswith only four memory components. However, a much higher number ofmemory components can be stacked, the number depending on the depth offield of the optical write/read device and how complex it is, but alsoon the parameters for the actual information carrying layer. Themechanical properties of the memory components, such as rigidity,friction and adhesive properties will also be capable of affecting theoptimal number of memory components in a stack and similarly the choiceof strategies for manoeuvring, moving and extraction of the memorycomponents and the mechanical solutions employed for this purpose. Inthis connection it should be understood that the not shown manoeuvringdevice which is not a part of the invention may well be in the form of aper se known mechanical gripping or translation mechanism, but may alsomake use of electromechanical, pneunomechanical or electropneumaticdesign solutions. Finally the number of memory components in a stackwill also be conditional on the desired random access time andwrite/read speeds.

For reading data from the data carrying area(s) there can be provided onthe surface of the memory component optically active structures, whoseconfiguration is substantially conformal with the data carrying areasand which moreover permit, e.g., the use of wavelength or angle-tunablemethods for reading data from the information carrying layer, thesebeing preferably arranged in layers between the optically activestructure and an underlying substrate. A data carrying area can therebyconsist of several information carrying layers provided at differentdepths in the memory component. In this connection the optically activestructures can be based on the use of refractive elements in the form ofmicrospheres, as these are described in International Published PatentApplication WO 91/11804. In the present method and the present datacarrying medium the use of microsphere-based optical structures (lenses)in connection with optical data storage would appear to be well suited,since it permits a high area density for the storage and permits greatdepth of field, thus enabling thin and flexible substrates to be used,while at the same time it is possible to achieve low friction and littletendency to sticking. It should also be noted that the memorycomponents, i.e. the disks or the cards, should be thin in order toprovide the desired high volumetric storage density.

What is claimed is:
 1. A data carrying medium for use with a method foroptical data storage with high density, comprising:a number of flat,thin memory components in the form of cards or disks which form a stackof memory components; each said memory component comprising at least oneinformation carrying layer; each said memory component comprising atleast one data carrying area, each said data carrying area including atleast one said information carrying layer for optical storage of data;the memory component outside each said data carrying area comprising atleast one optically transparent area; each said transparent area havinga geometric shape corresponding to a shape of a data carrying area; andeach said memory component in the stack of memory components beingalignable with each other to form a window area and being displaceablerelative to other memory components to permit reading and writingthrough said window area when said optically transparent area of saidmemory components are aligned with each other without separatingphysically each said memory component from said other memory components.2. The data medium according to claim 1, wherein at least two of saidmemory components are arranged in the stack, and each said memorycomponent is manoeuvreable in relation to other of said memorycomponents by manoeuvring means.
 3. The data carrying medium accordingto claim 1, including an optically active structure on the surface ofthe memory component at, at least one of each said data carrying area,said optically active structure forming a configuration which issubstantially conformed with each said data carrying area.
 4. The datacarrying medium according to claim 3, wherein each said data carryingarea comprises at least one of the information carrying layers arrangedin layers between the optically active structure and an underlyingsubstrate.
 5. The data carrying medium according to claim 1, wherein thememory component is a rectangular card.
 6. The data carrying mediumaccording to claim 1, wherein the memory component is a circular disk.7. The data carrying medium according to claim 1, wherein the memorycomponent is provided with at least one optically readable, uniqueidentification mark.
 8. A method for optical data storage with highdensity, wherein there are employed as a data carrying medium a numberof flat thin memory components, wherein said memory component comprisesat least one information carrying layer and comprises at least one datacarrying area which includes at least one said information carryinglayer and is adapted for optical data storage comprising the stepof:arranging at least two said memory components in a stack, forenabling each said individual memory component to be manoeuvered inrelation to other of said memory components by a manoeuvering device;forming a window area in the stack by providing at least one of anoptically transparent area on each said memory component, each said atleast one of said transparent area being arranged and designed in amanner that the transparent areas are aligned with one another andtogether forming the window area in the stack when the memory componentis arranged in the stack; displacing a given memory component inrelation to other of said memory components in the stack in at least oneof translation and rotation such that a data carrying area on the givenmemory component is aligned with the window area in the stack, andwithout the displacement causing the memory component to be separatedfrom the stack, whereby at least one of the data carrying areas whollyor partly is exposed for reading or writing by the manoeuvering devicein order to write or read data in the at least one of the data carryingareas; and optically addressing the memory component in the write orread operation without interference from the other memory components inthe stack.
 9. The method according to claim 8, includingdisplacing thememory component after the write/read operation back to its originalposition in the stack.
 10. The method according to claim 8,includingperforming the displacing of the given memory component bymeans of a rotary movement independently of the other memory componentsin the stack, the memory components and the stack, together with thesaid at least one of said window and said transparent area and datacarrying areas provided in the memory components being adapted for therotary movement.
 11. The data carrying medium according to claim 3,wherein the memory component is a rectangular card.
 12. A data carryingmedium for use with a method for optical data storage with high density,comprising:a number of flat, thin memory components in the form of cardsor disks which form a stack of memory components; each said memorycomponent comprising at least one information carrying layer; each saidmemory component comprising at least one data carrying area, each saiddata carrying area including at least one said information carryinglayer for optical storage of data; the memory component outside eachsaid data carrying area comprising at least one window; each said windowhaving a geometric shape corresponding to a shape of a data carryingarea; and each said memory component in the stack of memory componentsbeing alignable with each other to form a window area and beingdisplaceable relative to other memory components to permit reading andwriting through said window area when said window of said other memorycomponents are aligned with each other without physically separatingeach said memory component from said other memory components.
 13. Thedata medium according to claim 12, wherein at least two of said memorycomponents are arranged in the stack, and each said memory component ismanoeuvreable in relation to other of said memory components bymanoeuvring means.
 14. The data carrying medium according to claim 12,including an optically active structure on the surface of the memorycomponent at, at least one of each said data carrying area, saidoptically active structure forming a configuration which issubstantially conformed with each said data carrying area.
 15. The datacarrying medium according to claim 12, wherein each said data carryingarea comprises at least one of the information carrying layers arrangedin layers between the optically active structure and an underlyingsubstrate.
 16. The data carrying medium according to claim 12, whereinthe memory component is a rectangular card.
 17. The data carrying mediumaccording to claim 12, wherein the memory component is a circular disk.18. The data carrying medium according to claim 13, wherein the memorycomponent is provided with at least one optically readable, uniqueidentification mark.
 19. A method for optical data storage with highdensity, wherein there are employed as a data carrying medium a numberof flat thin memory components, wherein said memory component comprisesat least one information carrying layer and comprises at least one datacarrying area which includes at least one said information carryinglayer and is adapted for optical data storage comprising the stepof:arranging at least two said memory components in a stack, forenabling each said individual memory component to be manoeuvered inrelation to other of said memory components by a manoeuvering device;forming a window area in the stack by providing at least one window oneach said memory component, each said at least one window being arrangedand designed in a manner that the windows are aligned with one anotherwhen the memory component is arranged in the stack; displacing a givenmemory component in relation to other of said memory components in thestack in at least one of translation and rotation such that a datacarrying area on the given memory component is aligned with said windowarea in the stack, and without the displacement causing the memorycomponent to be separated from the stack, whereby at least one of thedata carrying areas wholly or partly is exposed for reading or writingby the manoeuvering device in order to write or read data in the atleast one of the data carrying areas; and optically addressing thememory component in the write or read operation without interferencefrom the other memory components in the stack.
 20. The method accordingto claim 19, includingperforming the displacing of the given memorycomponent by means of a rotary movement independently of the othermemory components in the stack, the memory components and the stack,together with the windows and data carrying areas provided in the memorycomponents being adapted for the rotary movement.
 21. The methodaccording to claim 19, including displacing the memory component afterthe write/read operation back to its original position in the stack.